The present invention relates generally to the field of semiconductor packaging processes and more particularly to cleaning processes for water-soluble fluxes used in soldering of flip chip semiconductor packaging and other electronic packages.
In the manufacture of integrated circuits, there is a continuing drive to fit more semiconductor devices and circuits in semiconductor wafers and electronic packaging assemblies, thus, driving denser, more complex semiconductor packages such as flip chip semiconductor modules and ball grid array (BGA) modules providing dense interconnection capability. The assembly of flip chip semiconductor devices and BGA modules in electronic packaging commonly involves the use of soldering processes. Fluxes play an important role is effective soldering processes by removing surface oxides from solder and metal pad surfaces to enable effective interconnection or solder joint formation during solder reflow.
Environmental concerns with previously used flux chemistries, such as rosin based fluxes or other fluxes that were cleaned after soldering using halogenated hydrocarbons or fluorocarbons, have driven the use of fluxes with a chemistry that is compatible with aqueous cleaning processes or mild, no clean fluxes that leave a non-conductive flux residue. Water-soluble fluxes generally provide a higher activity than no clean fluxes and are required for some electronic assembly processes. Water-soluble fluxes are typically composed of one or more activators to remove surface oxides, solvents to aid in deploying flux to the solder joint area, high temperature resistant chemicals, or vehicles that act as oxygen barriers and other additives (e.g., surfactants, thickeners, etc.). Water-soluble flux residues, if left after aqueous cleaning, may cause delamination of underfill from chip or substrate, and therefore, in most cases, it is desirable that water-soluble flux residues are removed after solder reflow and assembly processes.